Recording instrument for electrical measurements



July 16, 1940.

H.5ELL

RECORDING INSTRUMENT FOR ELECTRICAL MEASUREMENTS m m w M 92 N :W mm I 7J a m MR W W a w J .M Z d m w e 1 1N8 Rum Filed Oct, 20, 1957 Ba/ome/er"aCTerm/ha/a' Hsuwur SELL Ronye Je/ec/or' Patented July 16, 1940 azcoanmcmsrnmmm' roa'iiutc- TRICAL masmmmm'rs Helmut seii, Neubabelsberg, nearPotsdam, Gerassignor to Siemens & Halske, Aktienmm. geaellschai't,

Siemensstaiit, ne'ar Berlin, Germany, a corporation of GermanyApplication October 20,1937, Serial No. 169,940

In Germany October 24, 1936 8Claims.

The present invention relates to improvements in recording instrumentsfor electrical measurements.

The usual recording instruments for electrical measurements,particularly ink writers, have a power dissipation many .times greaterthan that of indicating measuring instruments, While a standardsensitive moving-coil measin'ing mechanism with scale has a powerdissipation of about 1 milliwatt when the pointer deflects to the end ofthe scale, an ink writer requires about 10 milliwatts. The use of inkwriters is, therefore, limited to cases where "sufilciently great torqueis v available. In each case the instrument must be adapted in aparticular manner to the purpose for which it is intended. Thisadaptation reiers above all to the moving coil for which resistances ofabout 1 to 20,000 ohms are usual.

In order to adapt the instrument to further purposes, special auxiliaryconnections, series resistances and shunts as well as rectifiers for theindication of alternating current may be employed. Series resistancesand shunts. as generally .used in indicating moving-coil measuringinstruments in order'to adapt a measuring mechanism to a large number ofcurrent and voltage measuring ranges for direct current or alternatingcurrent, are, as a rule, not suitable ifor ink resuch recorders.Besides, such arrangements would take up too large a space. Y 1

An object of the present invention is to provide an electrical measuringinstrument, particularly '5 a recording measuring instrument, which maybe adapted to a number of measuring ranges by means 01' simple auxiliarydevices in the same manner as the usual indicating moving-coil measuringinstruments are capable of being changed over. Another object oi theinvention, more particularly, is to provide such an adaptable recorderwhich has the same power dissipation as usual moving-coil instruments.

According to the invention the measuring or 5 recording mechanism withhigh power consumption is connected. through an amplifier oi. linearpower amplification ratio with a change-over apparatus which containsthe necessary auxiliary devices, and the power amplification ratio ofthe 50 amplifier is adjusted to a constant value in such a manner thatthe power dissipation corresponds I at most to the power dissipation oi.a standard indicating moving-con instrument.

To this end. bolometer amplifiers are particu- 5v laily suitable inwhich currents of air, which act corders owing to the high powerdissipation of.

on a bolometer bridge, are so controlled by a moving-coil measuringmechanism as to influence the bridge balance. 'Such an amplifier may beso designed that it operates without attendance and presents withinthenormal fluctuations 0i 5 the operating voltage a constant amplificationwith an error of less than 1%. Such an amplifier may be designed withinsuch small dimensions that it may be mounted in the casing of astandauxiliary devices. The amplification is then pref- 20 erably sorated that the voltage drop is not appreciably increased by theamplifier lying in the circuit 01' the indicating instrument. In such acase, it-is of advantage to connect the indicating moving-coil measuringinstrument, provided with the auxiliary devices, to the amplifier insucha manner that the resistance combination is not influenced by theconnection of the amplifier when changing the adaptation of theindicating moving-coil measuring instrument from one'to anothermeasuring range. This is possible by the use of compensating circuits.Here. a series connection must be employed in the case of a currentcompensating. circuit, and "a parallel connection in the case of avoltage compensating circuit. In this case, when changing over theindicating instrument to the individual measuring ranges or to difierentkinds of current, the indication of the ink writer or the like connectedthrough the amplifier a ees with the indications of the indicatinginstrument.

The invention will be further understood from the ifollowing descriptionof the embodiments illustrated in the accompanying drawings in whichFig. 1 shows in diagrammatic form an ink recorder combined with abolometric amplifier and connected with an auxiliary device containingan indicating instrument and change-over means for selecting themeasuring range, and

Fig. 2 shows another embodimentin which a change-over'device is directlycombined with an ink recorder arid a bolometric amplifier within, onecommon casing.

Referring at first to Fig. 1, numeral It indicates a unit comprising thefollowing elements. The moving coil 20 of an ink recorder carrying arecording pointer 2| and acting on a recording tape 22, is connectedthrough a resistor 30 to a diagonal point I of the bridge arrangement ofa bolometric amplifier. The magnet system coacting with the moving coil20 is represented by a permanent magnet 20. The bridge comprisesresistors 52, 53, 5 3 and 55, and has its other diagonal (points 3 and4) connected to terminals M and i2 which serve to connect the movingcoil 25 of the ink recorder to a direct current source. 55 designatesthe moving-coil and 50' the appertaining magnet of a measuring mechanismwhich bolometer bridge.

forms part of the bolometric amplifier. The coil 56 carries a vane 5|for thermically controlling the When the amplifier is in operation, theresistors 52, 53, 5d and 55 are exposed to the cooling influence of anair stream produced by an air blower of any appropriate type (notshown). A diaphragm 56 having slots 53 serves to restrict the aircurrent. While in the schematical illustration of thetemperature-responsive resisters 52, 53, 54 and 55, the vane 5|, and thediaphragm, these elements are shown at relatively large distances fromone another in order to render the diagram more easily understandable,it should be noted that in reality these elements are much closertogether and form a compact bolometric unit. The resistance of theresistors heated by the current flowing therethrough varies greatlyaccording to their temperature, and

' therefore depends on the cooling effect of the air current. When thevane 5| is in neutral posithe measuring range.

tion, both pairs of resistors 52, 54 and 53, 55 are cooled; to the samedegree. When the vane 5| moves in either direction, one set is cooledmore than the other and the resistances vary accordingly. As a result,very feeble currents actuating coil 50 and vane 5| suflice to bringabout corresponding changes of the diagonal voltage between points and 2of the bridge and of the comparatively great current intensities passingfrom the terminals II and I2 through the bridge to the moving coil 20 ofthe ink recorder, i. e., an effective amplification is ple ofamplification and a similar bolometric resistor-and-vane arrangementaredescribed in my Tl. S. Patent No. 1,944,721. The use of a bolometricamplifier to the invention has the advantage. over other types ofavailable amplifiers that it allbws obtaining extremely small dimensionsof the arrangement andthat it may easily be operated with lowdirect-current voltages which facilitates constructing portableinstruments.

Moving coil 50 is mounted in such a manneras to be as free as possibleof mechanical directingforces, 1. e., any biasing spring for holding thecoil in a neutral position is to be kept so feeble that its directingforce is negligible as compared with the torqueoriginating from theelectric currents. Coil 50 has one end directly connected with terminalpoint 5 of resistor 30, while the -.other end is connected with theother terminal point 5 of resistor 30 through a second resistor d0.Besides, the ends of the moving coil 50 are directly connected with theinput terminals l3 and Hi of unit id.

The second-unit 50 consists of a standard indicating instrument of themoving-coil type"which is equipped with means for selectively changingThe moving coil of this its pointer by 1| The moving coil instrument isindicated by 10, and its magnet system by i0.

produced. This princiin arrangements according for instance ment isalways auxiliary 60 are H and M of unit I.-

known per se, for instanceby'U. S. Patent No. 1,811,319. Instead of theillustrated form, others may be used, for instance those havingselectable shunt resistors if voltages are to be measured.

The measuring instrument 6|! by proper adapta tion of the resistances ofits individual elements is so designed that in the case of a constantdeflection of the moving coil, always the same current corresponding tothe sensitiveness of the measuring mechanism flows in the moving coil,independently of the measuring range switched in. This current flows 50of the bolometer amplifier. The movement of the control vane 5| causedby the current brings the bridge out of balance, whereby a correspondingcurrent is passed through the moving coil 20 of the ink recorder. If acurrent J flows in the moving coil 20, it divides itself into a-currenti which flows through the resistorjfl and current J-i flowing in theresistor 30. The current J-i produces in the resistor 30 a voltage drop(J-i) Rn, if Rn is-the ohmic value oi the resistor 30.

The moving coil 50 now moves so long as the voltage acting thereupondeparts Iromthe zero value and remains therefore in a position in whichthis voltage is equal to zero. The zero value occurs if the voltage dropacross the resistor 30 is equal to the voltage drop across theresistor40. Since the latter is traversed by the current i, the correspondingvoltage drop is 2'.Rv, if Rv is the ohmic value of the resistor 40. Thefollowing equation is then obtained:

I R the consumption of current of the indicating instrument enclosed by60 amounts to 0.3 milliampere for the end deflection and the consumptionof current of the ink recorder through the moving coil amounts to 15milliamperes, the amplifier will be adjusted to 50 times the normalcurrent amplification. To this .end, the resistances 30 and 40 will berated for 1 and 50 ohms respectively. In this manner, the deflection ofthe inker measuring mechanism 20 is proportional to that of theindicating measuring instrument III, independently of the adjustment ofthe measuring range selector 90.

This is due to the fact that in the present case of a cm'rentcompensating circuit, the resistance of the current branchseries-connected to the measuring mechanism oi! the indicatinginstruadjusted to the zero value automatically. However, if a circuit isemployed inwhich the resistance of the corresponding current branch isalways adjusted to the value we automatically,'the current branch mustbe parallel-connected to the measuring mechanism of theindicatinginstrument. in order to avoid during the change-over aninfluencing oi the refistance combination. 1

r the. ink recorder.

- foregoing explanations made of Fig. 1.

An auxiliary indicating instrument III; Il may be dispensed with and thebolometer amplifier may be directly connected to the auxiliary devicesfor changing over to the different measuring ranges. In this case, it isfurther possible to arrange the means for selecting the measuring rangewithin the casing ill of the ink recorder.

An embodiment of this type is shown in Fig. 2. The instrument I containsinput terminals '63 and 64 to be connected with the circuit, thecurrentoi' which is to be measured, and terminals II and I! forconnecting-an auxiliary direct current source furnishing the current foroperating Since the individual elements are numbered, identically withthe corresponding elements of Fig. 1, the arrangement of Fig. 2 and itsfunction will be easily understood from the The bolometric amplifier ofFig. 2 also has the same construction already described with referenceto Fig. 3.

The invention is also applicable if instead of an ink' recorder anotherapparatus of relatively high power consumption is employed which is tobe adapted to difl'erent selectable ranges of input currents orvoltages.

I claim:

1. In an electric measuring system for operating a recording mechanismin proportion to input magnitudes furnishing a power lower than thepower consumption of the mechanism, in combination, variable resistancemeans for selectively adapting the system to different measuring ranges,said resistance means having term nals for supplying the magnitude to bemeasured, an amplifier having a movable control member, an input circuitfor actuating said control member, said input circuit being connectedwith said variable resistance means, and an output circuit connectedwith said recording mechanism, said output circuit comp ising means forsupplying auxiliary power to said mechanism and means I controlled bysaid movable member for varying said power, a resistance arrangementconnected with said input circuit and said output circuit andinteriinking said two circuits so as to form a balancing network forcompensating the efiect of said magnitude on said input circuit by acounter-magnitude caused by said output circuit when said movablecontrol member is deflected in proportion to said magnitude. V

2. In a system for determining an electric magnitude, in combination, amechanism to be operated in response to said magnitude and having a highpower consumption as compared with that furnished by said magnitude, achange-over de;

'vice connected 'withsaid mechanism for selecting.

its measuring range in accordance with said magnitude, said devicehaving input terminals for supplying said magnitude, an amplifyingarrang'ement having a movable control member, an input circuit foractuating said control member, said input circuit being connected withsaid change-over device, and an output circuit connected with saidmechanism, said output circuit comprising means for supplying auxiliarypower to said mechanism and means controlled by said movable member forvarying said power, and impedance means arranged between said changeoverdevice and said amplifying arrangement and connected with said inputcircuit and said-output circuit so as to interlink said circuits to forma balancing network for compensating the eii'ect of said magnitude onsaid input circuit by,a countermagnitude furnished by said' power sourcethrough said output circuit when said movable member is adjusted inaccordance with said] magnitude.

- 3. In an arrangement for determining an electric magnitude, incombination, two separate units electrically cooperating with eachother, one of said units consisting of a moving-coil measuringinstrument having input terminals for supplying said magnitude, aresistance device for selecting the measuring range, a moving-coilmeasuring mechanism and output terminals connected with said mechanism,said other unit containing a mechanism to be operated in accordancewithsaid magnitude and having a high for supplying auxiliary power to saidmechanism and means controlled by said movable member for varying saidpower, and impedance means arranged between said change-over device andsaid amplifying arrangement and connected with said input circuit andsaid output circuit so as to interlink said circuits to form a balancingnetwork for compensating the eflect of said magnitude on said inputcircuit by a counter-magnitude furnished by said power source throughsaid output circuit when said movable member is adjusted in accordancewith said magnitude.

4. In a system for determining an electric magnitude, in combination, amechanism to be operated in response to said magnitude and having a highpower consumption as compared with that furnished by said magitude, achange-over device for adapting the measuring range of said mechanism tosaid magnitude, said'device'being designed to be supplied with saidmagnitude and a power consumption in an order of magnitude of at mostthat of a usual indicating measuring instrument of the moving-coil typeand being connected with said change-over device so as to ,be operatedby the magnitude to be determined after its passage through said device,and an impedance combination arranged between said change-over deviceand said amplifying arrangement and interlinking said input circuit andsaid .output circuit so as to form a self-balancing system wherein theeffect ofsaid magnitude on said control means is balanced by acounter-magnitude furnished by the current in said output circuit.

5. In a system for determining an electric magnitude, in combination, amechanism to be operated in response to said magnitude and having a highpower consumption as compared with that furnished by said magnitude, achange over device for adapting-the measuring range-oi said mechanism tosaid magnitude, said device having input terminals for supplying saidmagnitude, means for supplying an auxiliary current, a bolometricamplifier comprising a bridge arrangement of thermo-responsiveresistors, said bridge having its input diagonal connected with saidcurrent supply means and its output diagonal connected with saidmechanism, control means for varying the thermal conditions of saidbridge arrangement, said control means having a moving coil forming theoperating element of said control means and having a power consumptionadapted to said magnitude to be determined, said moving coil beingconnected with said change-over device, and a resistance combinationconnected between said bridge and said change-over device so as to forma balancing network for compensating the effect of said magnitude onsaid control means when the position of said moving coil is inaccordance with said magnitude.

6. In a system for recording an electric magnitude, in combination, arecording mechanism, a resistance device for selecting the measuringrange of said recording mechanism, said device being arranged to besupplied with the magnitude to be measured, means for supplying anauxiliary current, abolometric amplifier having a thermosensitiveresistance bridge and a movable control member for varying the thermalcondition of said bridge, said bridge having an input diagonal connectedwith said current supply means and its output diagonal connected withsaid recordin mechanism, said control member being connected with saidresistance device, a resistor series connected with said recordingmechanism and said output diagonal, and a second resistor connected,with said first resistor and said control member so as to branch oflfrom a point between said first resistor and said recording mechanism,said second resistor having a higher resistance than said firstresistor, the ratio or said resistances being similar to that of thepower consumption of said recorder mechanism and said control member.

7. In a system for determining an electric magnitride, a moving-coilmeasuring instrument of low power consumption designed to be suppliedwith said magnitude and, having change-over means for adapting themeasuring range of said 7 connected with a point be adjusted inaccordance with said magnitude, a bolometric amplifier having athermo-responsive resistancearrangement connected with said apparatusand a movable control member for thermally control member beingconnected with said measuring instrument and having a. power consumptionsimilar to that oi said instrument, and a resistance combinationinterlinking the circuit of said apparatus and the circuit of saidcontrol member so as to form a current-balancing network forcompensating the effect of said magnitude on said control member by partof the current operating said apparatus when said apparatus is adjustedin accordance with said magnitude.

8. In a system for determining an electric magnitude, a moving-coilmeasuring instrument of low power consumption designedto be suppliedwith said magnitude and having change-over means for selecting themeasuring range of. said instrument, in combination with an apparatus ofhigh power consumption to be operated in accordance with said magnitude,a bolometric am plifler having a. thermo-responsive resistancearrangement connected with said apparatus and a movable control memberfor thermally biasing said resistancearrangement, said control memherbeing connected with said measuring instrument and having a powerconsumption similar to that of said instrument, a resistor series con--neeted between said apparatus and said resistance arrangement, and asecond resistor having one end connected with a point between said firstresistor and said apparatus and the other end between said controlmember and said measuring instrument, said second resistor having ahigher resistance than said first resistor, ances being similar tothatof the power consumptions of said apparatus andoi said instrugment,said two resistors being dimensioned so as to neutralize the eflect ofsaid magnitude on said control member when the condition oi saidapparatus is in conformity with said magnitude,

nnmlni'r SELL.

biasing said resistance arrangement, said and the ratio of said resist-

